Fluids, such as gases and liquids within an enclosed space such as a tank or building, are in many cases required to be circulated or mixed, and to be exchanged with other fluids in order to maintain a predetermined content or concentration. For example, the ventilation of a building requires that the air within the building be circulated, and that such air may be exchanged as it becomes stale, or too hot or too cold, or too dry or too humid, etc., and replaced with fresh air, in order to maintain a desirable condition within the building or space. There are numerous complex mechanisms whereby these objectives may be achieved. However, in many cases it is desirable to achieve these objectives at a much lower cost than is possible using existing equipment. For example, in agricultural buildings, industrial buildings, warehouses and the like, it is desirable to provide efficient air circulation within the building space, and at the same time to ventilate it by removing some of the air and replacing it with fresh air. Due to variations in climatic conditions, the rate at which such building air is removed and replaced with fresh air may vary widely. Variation may take place during a single day or as between day and night.
In many cases, older buildings did not provide any means for automatic ventilation and fluid exchange in this way so as to achieve these results. In order to bring such older buildings up to up-to-date standards, or if such older buildings are modified to provide for a different usage for such building, then it is frequently desirable to instal such exchangers in the walls or roof of the building, at minimum cost, and with a minimum disruption of the existing building fabric.
Some such fluid exchangers are shown in U.S. Pat. Nos. 3,302,548 and 4,079,665. The devices shown in these patents provide for an exchanger type of device which may readily be installed in a suitable opening in the wall or roof of the building, and which may be operated to provide air circulation within the building, and simultaneously, to remove varying proportions of air and replace the air with fresh make-up air from the exterior.
Such devices generally speaking operate by means of one or more fans powered by electrical motors, and are required to operate at fairly high speeds. This is because in order to provide adequate ventilation throughout a relatively large building, such as an agricultural building, warehouse or the like, it is necessary to eject air by means of such a fan at a considerable velocity in order to achieve distribution across the building. Where the device is being operated in a recirculating mode, i.e. a proportion of air is being withdrawn from the building, and is then simply being recirculated back into it, with a proportion of make-up air, then the air flow stream within the device is required to turn through 180.degree., in a relatively confined space.
The majority of these earlier devices involved one or more flat surfaces set at an angle to the air flow stream, to effect the 180.degree. change in flow path. Consequently the air flow tended to develop a large degree of turbulence. This materially reduced the efficiency of the device. Accordingly, in order to obtain the necessary high velocity ejection of air into the building, it was necessary to use heavy duty fans and motors in an attempt to overcome these inefficiencies.
Clearly, it would be desirable to reduce resistance and improve the efficiency of the device, by improving the flow characteristics. In this way a greater degree of air distribution could be effected using the same horse power, or conversely, the same distribution could be achieved while reducing the horse power. The efficiency of the fans and motors could thereby be utilized to a much greater degree, achieving greater air distribution throughout the building. In this way, it might for example be possible to reduce the number of such installations required to provide complete ventilation within a large building space or provide a savings in power consumption.
In order however to make these improvements in a cost efficient manner, it must clearly be done at a manufacturing cost which is no greater than, and preferably less than that of the earlier devices.
It must also be born in mind that these devices are required to operate in widely varying climatic conditions and in different situations. In the particular case of buildings housing agricultural stock, the animals are frequently kept within the building 24 hours a day throughout the winter months, at least, and in some case throughout the entire year. The animals are known to generate considerable heat and humidity within the building. The air around them must be thoroughly circulated and ventilated at all times in order to maintain the animals in good health. In addition, however, the handling of air streams being ejected from such buildings containing substantial quantities of humidity, poses certain problems in the colder months. The humid air upon being ejected through the building wall at high speed, tends to produce heavy condensation within the air circulation device, leading to a rapid build-up of ice such that air passage through the device may be blocked, or the operating parts of the device may become seized.
A further typical problem existing with this type of equipment is the requirement for simplicity of service. Generally speaking, the equipment is required to operate 24 hours a day, 7 days a week. In the event of breakdown, it is highly desirable that the owner of the building shall himself be capable of simply installing replacement components so that the unit may continue to function. Buildings of this type are frequently located in remote areas. Servicing by trained service technicians in such areas is a costly factor which must be eliminated as far as possible.
For all of these reasons it is highly desirable that the design and manufacture of the device shall be as simple as possible, so that it may be readily dismantled and reassembled using conventional hand tools, such as would be available to any owner.
Such devices desirably incorporate temperature sensors, and automatic servo controls, such that the temperature of the air exiting from the building may be monitored, and the setting of the exchanger device may be adjusted by the servo control, so as to maintain the temperature or humidity level within the building at a predetermined range. Where any portion of such temperature controls are liable to failure in use, it is however desirable that if possible they may simply be disconnected, and the exchanger portion of the device set by hand so that it may continue to operate to give some degree of ventilation, until a technician has rectified the problem.